The present invention relates to magnetic structures, including magnetic yokes for inductors, and methods of making a magnetic inductor having low magnetic loss at high frequency capable of use for an on-chip power converter.
Thin film ferromagnetic inductors can be used as energy storage devices for ICs (integrated circuits). High energy storage is required for power management on chips. Miniaturization of magnetic inductors and integration on semiconductor chips requires the choice of high performance magnetic materials.
The integration of power converters onto a supporting substrate, for example silicon, is one path to reduce the cost, weight, and size of electronic devices. A challenge for developing fully integrated power converters, however, is the development of high quality thin film inductors. To be viable, the inductors should have high Q (Q factor or quality factor), large inductance, and/or large energy storage per unit area. Furthermore, it is necessary that such inductors employ magnetic materials that have soft magnetic properties with low coercive force (for example, an Hc less than 1.0), high saturation magnetization, high resistivity (for example, greater than or equal to 110 mohm-cm) in order to reduce inductor losses at high frequencies from eddy currents. It is also desirable that such magnetic materials have excellent thermal stability with respect to processing temperatures that can be dictated by the integration process on-chip, for example, temperatures of about 250 to 300° C.